Recently, various recording systems have been developed with the development of office automation. Among these, thermal recording systems with which the noise during printing is small and the operation is simple are drawing attention. In the thermal recording system, a thermal recording apparatus such as a thermal printer is used. A recording paper and a heat-sensitive ink layer of an image transfer material are contacted and the film is selectively heated by pulse signals generated from a heating head opposite to the ink layer. The ink heated via the film is melted or sublimated so as to be transferred to the recording paper.
As the image transfer material, thin plastic films are generally used for promoting thermal efficiency. However, in cases where a plastic film is used as the base film of the image transfer material, a part of the film is melted by the heat given by the thermal head and the melted plastic sticks to the thermal head. This phenomenon is called sticking phenomenon. If this phenomenon occurs, not only the image transfer material does not run smoothly, but also the thermal head is severely stained, so that the clearness of the printed characters is degraded. To avoid the sticking phenomenon, it has been proposed to give various surface treatments to the surface of the plastic film, which contacts the thermal head. For example, those having a heat-resistant protective layer made of silicone, melamine resin, phenol resin, epoxy resin, polyimide or the like (Japanese laid-open patent application (Kokai) No. 55-7467) and those having a sticking-preventing layer made of an inorganic pigment with a high activity and a resin with high heat-resistance (Japanese laid-open patent application (Kokai) No. 56-155794) were proposed. Further, those in which a layer made of a water-soluble or water-dispersible silicone and a resin is provided (Japanese laid-open patent application (Kokai) No. 60-192628), those in which a layer made of a water-dispersible fluorine-contained resin and a water-soluble polymer (Japanese laid-open patent application (Kokai) No. 60-192630), and those in which a wax and/or a liquid or a substance which is in the form of liquid or paste at room temperature is applied or transferred (Japanese laid-open patent application (Kokai) Nos. 59-148697 and 60-56583) have been disclosed.
However, with those having a heat-resistant protective layer, since the slipping between the film and the head is insufficient, the running property of the thermal transfer ribbon is poor in printers with low pulse width or in printers of platen-driving type, so that printing blot may be formed and, in an extreme case, the running of the ribbon is stopped.
With the films to which an inorganic pigment is added, the lifetime of the head is shortened due to the friction between the film and the head. Further, since the surface of the film is rough, heat-conductivity is low, so that clearness of the printed characters is poor. With those in which silicone resin or fluorine-contained resin is coated, by winding the film into a roll, the resin is likely to be transferred to the surface to which ink is to be applied, so that the film may shed the ink when the ink is applied to the film or the adhesion of the ink to the film may be poor.
Although the laminated films prepared by applying a wax or the like on a plastic film and drying the wax exhibits good slipping between the film and the head, the slipping between the film and the fixing shafts of the printer is poor, so that sticking may occur in the event.
On the other hand, conventional heat-sensitive mimeograph stencils typically comprises a film for heat-sensitive mimeograph stencil and a porous support adhered to the film with an adhesive. Conventional films for heat-sensitive mimeograph stencil includes vinyl chloride-vinylidene chloride copolymer films, polypropylene films and polyethylene terephthalate films. Recently, for promoting the sensitivity, the film was made thin and other improvements were made as described in Japanese laid-open patent application (Kokai) Nos. 62-149469 and 63-312192. As the porous support, tissue paper and polyester gauze have been used.
These laminates are overlapped with an original carrying characters or figures and infrared flash is irradiated thereto. As a result, the portions of the characters or figures are melted by absorption of heat and holed. The thus holed original is used as a stencil for printing. Recently, the holing is also carried out by using a thermal printer. In this method, a thermal head is contacted with the film and printing energy is given to the film according to the same principle as in the ordinary thermal image transfer system so as to hole the film. Thus, in the above-described flash-irradiation method, good release from the original is required, and in the thermal method, anti-sticking property is required as in the heat-sensitive image transfer material.
However, in cases where a plastic film is used as a film for heat-sensitive mimeograph stencil, the sticking phenomenon due to the heat given to the film by the thermal head is generally observed. This phenomenon causes poor running of the film and staining of the thermal head, which degrade the clearness of the holing, as in the case of heat-sensitive image transfer material. On the other hand, in cases where the holing is carried out by using a flash lamp, the film and the original may be fused. To eliminate this, releasing layer or anti-sticking layer is formed. However, when the film is used for mimeograph stencil, the releasing layer or the anti-sticking layer is required to be easily melted by heat. Therefore, if the above-mentioned heat-resistant protective layer is used, the holing may be non-uniformly conducted or, in an extreme case, holes are not formed.